As a head lamp light source for a vehicle for improving visibility of a driver in the nighttime, a high intensity discharge lamp (HID lamp) is known.
This HID lamp can obtain brighter light than a conventional halogen lamp, etc., with small power, whereas it requires an operating device specific to the HID lamp which is different from the conventional lamp.
Furthermore, this operating device also needs to satisfy specific conditions as the device for a head lamp of a vehicle. That is, the head lamp for a vehicle must output a stable, high intensity light beam in a short time.
Immediately after the ignition of the lamp, the operating device generally needs to supply lamp power at least twice rated power. FIG. 5 shows this condition in which in contrast to rated power of 35 W, power of approximately 70 W is required immediately after the ignition.
Thus, because of the special circumstance that the lamp needs to be supplied with high power immediately after the ignition so as to function as the operating device for the head lamp for a vehicle, a DC-DC converter circuit of the operating device also needs to be designed to be able to supply high power at the time of ignition.
On the other hand, in order to further improve the safety of more drivers, not only medium-size cars and full-size cars but also popular cars and light cars are required to mount the HID lamp in the future and in line with the demand for reductions in the size and weight of vehicles in recent years, it is an urgent task to reduce the size and weight of the operating device.
In order to reduce the size and weight of the operating device, an effort is conventionally underway to reduce the size and weight of the operating device by reducing the diameter of the winding of a DC-DC converter transformer and thereby reducing the size of this transformer.
Though a reduction in the diameter of the winding involves a problem of heat generation, the aforementioned measures are adopted giving priority to reductions in the size and weight of the DC-DC converter transformer on condition that greater power can be supplied exclusively for a predetermined period from the ignition.
On the other hand, promoting reductions in the size and weight of the DC-DC converter transformer requires the size of a core part which makes up a large proportion of the weight of the transformer to be reduced.
However, attempting to reduce the size of the core part of the DC-DC converter transformer having the structure of the conventional DC-DC converter circuit increases the tendency of magnetic saturation to occur, preventing large power necessary to operate the lamp from being obtained. That is, the aforementioned special circumstance for allowing the device to operate as the operating device for a head lamp of a vehicle constitutes considerable hindrance in reducing the size of the core part, and for this reason reductions in the size and weight of the operating device have been limited to minor reductions in the size and weight of the above described winding.
The present invention has been implemented in view of such circumstances and it is an object of the present invention to provide a high intensity discharge lamp operating device for operating a HID head lamp for a vehicle capable of reducing the size and weight of a DC-DC converter circuit, and accordingly of the operating device without generating any magnetic saturation of a transformer core part even when igniting the lamp.